Anxiety disorders are associated with high use of health care services and poor health outcomes. When anxiety disorders occur in combination with other serious psychiatric and medical illnesses, the result may be high personal and social costs, in terms of both increased utilization of services and additional morbidity. Although there is evidence that comorbid anxiety disorder complicates the course of disease in both depressed and medically ill patients, very little is known about how this affects long term functioning and well-being and use of health care services. We propose to conduct secondary analyses of data from the Medical Outcomes Study (MOS) to examine the effects of comorbid anxiety disorder (panic, phobia, and generalized anxiety disorder) on use of services, use and quality of prescribed medications, and change over time in functioning and well-being, anxiety symptoms, course of depression, adherence to medical recommendations, and satisfaction with care in patients with depressive disorder or a serious medical condition (diabetes, heart disease, or hypertension). We will test whether the impact of comorbid anxiety disorder on outcomes is greater among those with depression or chronic medical illness. Because the prevalence of comorbid anxiety disorder is also important for determining impact, the prevalence of comorbid anxiety disorder and anxiety symptoms will be estimated in MOS patient groups. In addition, the role of factors such as treatment style, quality of care, and external factors (e.g., social support, coping style) in mediating the effects of comorbid anxiety on outcomes will be explored. The analyses use data from a large, representative, longitudinal sample of patients typical of those seen in everyday practice in both mental health specialty and primary care settings. The analyses will use regression models controlling for patient characteristics as well as disease severity and comorbidity.